Mechanism of Signal Transduction in Tumor Necrosis Factor-Like Weak Inducer of Apoptosis-Induced Matrix Degradation by MMP-3 Upregulation in Disc Tissues

Study Design. Molecular biologic and immuno-histologic analyses using in vitro murine intervertebral disc tissue culture. Objective. To investigate the role of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in matrix metalloproteinase 3 (MMP-3) pathway induction, and the effect of TWEAK to induce other cytokines or angiogenesis factors in disc tissues. Summary of Background Data. We previously demonstrated that TWEAK and its receptor Fn14 were expressed in murine disc tissues. TWEAK induced MMP-3 upregulation and aggrecan downregulation in disc tissues. Methods. Enzyme-Linked ImmunoSorbent Assay (ELISA), western blot, and immuno-histologic analyses were used to assess the role of TWEAK-induced MMP-3, using murine disc tissue culture. Results. TWEAK induced disc cells to generate MMP-3 as did TNF-&agr; and IL-1&bgr;. MMP-3 activity was detectable in murine disc cells. MMP-3 induction was markedly inhibited with a c-Jun N-terminal kinase (JNK) inhibitor. Phosphorylation of JNK was also confirmed. Introduction of TWEAK resulted in the degradation of disc matrix in organ disc culture, whereas proteoglycan degradation was markedly abrogated in the presence of an MMP-3 specific inhibitor or a JNK inhibitor. In addition, TWEAK also induced monocyte chemotactic protein (MCP)-1 via the NF-&kgr;B pathway, as phosphorylation of NF-&kgr;B was confirmed by western blotting. Conclusion. TWEAK plays an important role in MMP-3 induction in murine disc cells via JNK that results in degradation of disc matrix. TWEAK also induces MCP-1, which belongs to the chemokine family that recruits inflammatory cells via the NF-&kgr;B pathway.